This invention relates generally to gas turbine engines and more particularly to identification of turbine blades having internal features. In gas turbine engines, fuel is combusted in compressed air created by a compressor to produce heated gases. The heated gases are used to turn turbine blades, or airfoils, to produce rotational power for, among other things, operating the compressor. During operation of the gas turbine engine, temperatures inside the combustion chamber can reach 2500° F., resulting in the blades being subject to temperatures in excess of 1700° F. In order to cool the turbine blades, relatively cooler compressed air that bypasses the combustion chamber, or bleed air, is forced through internal passages of the blades. The passages include pathways or channels having various geometries in order to direct the bleed air throughout the interior of the blade. The bleed air flowing through the passages maintains a temperature gradient throughout the entirety of the blade at which the blade can properly function.
For performance or manufacturing reasons, it is sometimes necessary to change or modify the interior features of a particular blade model. Meanwhile, the exterior of that blade must be maintained the same in order to meet the design of the specific gas turbine engines in which that model of blade is used. Traditionally, a model number that identifies the interior features of the turbine blade is cast on the exterior of the turbine blade casting. The cast model numbers produce a shallowly indented number on the surface of the turbine blade. The shallow numbers do not create any protrusions or cavities that upset the balance of the blade while it is rotating. Any, even small, disproportion of weight along the length of the turbine blade can produce vibrations during the high-speed rotations produced in gas turbine engines.
While the cast model numbers are small enough to prevent any interference with the operation or installation of the blade, the numerals are often illegible and confusingly similar. For example, a cast “9” may look like a “0.” Thus, a turbine blade having second generation internal features would look identical to a turbine blade having first generation internal features, and there would be no positive way to identify which generation of internal features it possesses. Therefore, blades could be improperly introduced into the production stream where they would receive incorrect finishing procedures that are not discovered until a later time. It is desirable for production cost and safety considerations to completely eliminate the possibility of these mistakes. There is, therefore, a need for a turbine blade having an identification feature that unmistakably identifies the internal features of visually identical turbine blades without interfering with the operation of the blade itself.